1 00:00:11,828 --> 00:00:13,030 Earth... 2 00:00:13,600 --> 00:00:15,700 the only planet orbiting the sun 3 00:00:15,770 --> 00:00:17,770 that has continents, 4 00:00:17,840 --> 00:00:19,510 oceans, 5 00:00:19,580 --> 00:00:21,140 plate tectonics, 6 00:00:21,210 --> 00:00:23,680 and the sole planet with an atmosphere 7 00:00:23,750 --> 00:00:28,050 that has sustained life for billions of years. 8 00:00:28,120 --> 00:00:30,380 How did Earth get this way? 9 00:00:30,450 --> 00:00:33,650 What's behind the power, the violence 10 00:00:33,720 --> 00:00:36,420 that cracks solid rock in an instant, 11 00:00:36,490 --> 00:00:38,930 that shatters buildings 12 00:00:38,990 --> 00:00:42,000 and sends tsunamis racing for the shore, 13 00:00:42,060 --> 00:00:47,100 that erupts seas of lava and billowing clouds of ash? 14 00:00:49,810 --> 00:00:52,140 Earth has been making headlines lately. 15 00:00:52,210 --> 00:00:55,710 Powerful images of destruction never seen in our lifetime. 16 00:00:55,780 --> 00:00:57,480 People are asking, 17 00:00:57,550 --> 00:01:02,920 "has Earth entered a period of intense geologic upheaval?" 18 00:01:02,990 --> 00:01:06,590 Scientists have new answers to questions about our home, 19 00:01:06,660 --> 00:01:09,960 the third planet from the sun. 20 00:01:10,030 --> 00:01:12,630 It's a story that, just a few decades ago, 21 00:01:12,690 --> 00:01:15,060 could not have been told. 22 00:01:24,710 --> 00:01:26,170 About 10 billion years 23 00:01:26,240 --> 00:01:28,940 after the big bang created the universe, 24 00:01:29,010 --> 00:01:33,250 our solar system began to form. 25 00:01:33,320 --> 00:01:35,750 Scientists calculate that this happened 26 00:01:35,820 --> 00:01:40,350 4.567 billion years ago, 27 00:01:40,420 --> 00:01:45,090 and that was when planet Earth was created. 28 00:01:45,160 --> 00:01:49,200 A long time ago, about 4 1/2 billion years ago, 29 00:01:49,260 --> 00:01:53,300 the Earth formed from this nebula around the sun. 30 00:01:53,370 --> 00:01:57,500 The sun in the center, and the nebula swirling around, 31 00:01:57,570 --> 00:02:01,110 and the bits of the nebula accreting, 32 00:02:01,180 --> 00:02:04,480 that is, sticking together and colliding with each other, 33 00:02:04,550 --> 00:02:08,450 and it was a very turbulent time. 34 00:02:11,650 --> 00:02:15,060 And the Earth gradually came together, 35 00:02:15,120 --> 00:02:17,190 and as it became more massive, 36 00:02:17,260 --> 00:02:20,060 the gravitational force became larger, 37 00:02:20,130 --> 00:02:23,660 and it could attract more of the small pieces, 38 00:02:23,730 --> 00:02:26,570 and the Earth grew and grew. 39 00:02:29,240 --> 00:02:31,300 It took about 100 million years 40 00:02:31,370 --> 00:02:34,870 for Earth to reach its present size, 41 00:02:34,940 --> 00:02:36,410 but before it did, 42 00:02:36,480 --> 00:02:41,880 our planet experienced its largest, most dramatic event. 43 00:02:41,950 --> 00:02:43,820 So after the early Earth formed, 44 00:02:43,890 --> 00:02:45,720 probably tens of millions of years afterwards, 45 00:02:45,790 --> 00:02:48,660 you had a Mars-sized object that actually hit the Earth. 46 00:02:54,600 --> 00:02:57,600 The giant planetoid impactor was called theia. 47 00:03:00,040 --> 00:03:02,670 The Mars-sized impactor hit the Earth, 48 00:03:02,740 --> 00:03:05,410 and it spewed off a lot of the material from the Earth, 49 00:03:05,470 --> 00:03:07,110 and part of that formed the small... 50 00:03:07,180 --> 00:03:08,980 The moon that we now have. 51 00:03:09,040 --> 00:03:11,580 And also we generated a lot of heat from this impact, 52 00:03:11,650 --> 00:03:14,810 and so it might have remelted a lot of the early Earth. 53 00:03:17,850 --> 00:03:19,490 Scientists only recently learned 54 00:03:19,550 --> 00:03:21,220 of this massive impact 55 00:03:21,290 --> 00:03:24,660 by studying rocks collected on the moon. 56 00:03:24,730 --> 00:03:27,230 It turned out that the moon rocks were very similar 57 00:03:27,300 --> 00:03:30,830 in composition to Earth rocks. 58 00:03:30,900 --> 00:03:34,230 After the impact, the moon became a satellite, 59 00:03:34,300 --> 00:03:37,840 while the Earth was left a molten ball of fire. 60 00:03:39,510 --> 00:03:43,040 And so the early Earth was, like, this molten mass. 61 00:03:43,110 --> 00:03:47,680 That must have looked liked maybe one giant volcano 62 00:03:47,750 --> 00:03:49,050 or lava lake. 63 00:03:51,320 --> 00:03:54,820 It slowly solidified and formed this outer crust 64 00:03:54,890 --> 00:03:57,690 that is where we stand today. 65 00:03:59,460 --> 00:04:01,330 As the crust formed, 66 00:04:01,400 --> 00:04:04,230 collisions and bombardments died down, 67 00:04:04,300 --> 00:04:07,600 but the meteorites continue to fall to this day. 68 00:04:07,670 --> 00:04:09,840 We start with some breaking news this hour. 69 00:04:09,910 --> 00:04:11,770 People in the Urals in Russia 70 00:04:11,840 --> 00:04:14,710 have seen burning objects raining down from the sky 71 00:04:14,780 --> 00:04:17,210 after a meteorite exploded above the Earth, 72 00:04:17,280 --> 00:04:19,150 causing a meteor shower. 73 00:04:19,210 --> 00:04:22,080 Eyewitnesses reported several blasts. 74 00:04:24,990 --> 00:04:28,790 Despite the shock that a meteor shower can cause, 75 00:04:28,860 --> 00:04:32,030 meteorites are extremely valuable to scientists 76 00:04:32,090 --> 00:04:35,560 who study when the Earth was created. 77 00:04:35,630 --> 00:04:39,270 They are collected and studied worldwide. 78 00:04:39,330 --> 00:04:41,770 But the best place to find these rocky aliens 79 00:04:41,840 --> 00:04:46,540 is one of the Earth's most unearthly places: 80 00:04:46,610 --> 00:04:47,670 Antarctica. 81 00:04:50,710 --> 00:04:52,550 On the sleek, blue ice expanse 82 00:04:52,610 --> 00:04:55,120 of the central antarctic ice sheet, 83 00:04:55,180 --> 00:04:59,420 the surface is swept clean by relentless winds. 84 00:04:59,490 --> 00:05:03,790 A meteorite sits exposed for an average of 20,000 years, 85 00:05:03,860 --> 00:05:06,460 sometimes for several million years, 86 00:05:06,530 --> 00:05:10,230 before scientists might spot it and collect it. 87 00:05:12,100 --> 00:05:14,400 A type of meteorite called a chondrite 88 00:05:14,470 --> 00:05:16,470 contains the same basic elements 89 00:05:16,540 --> 00:05:19,240 that make up the sun and planets, 90 00:05:19,310 --> 00:05:21,310 so they tell US a great deal 91 00:05:21,380 --> 00:05:23,940 about where we originally came from 92 00:05:24,010 --> 00:05:27,180 and when. 93 00:05:27,250 --> 00:05:30,080 To figure out how old meteorites and the Earth 94 00:05:30,150 --> 00:05:31,820 actually are, 95 00:05:31,890 --> 00:05:34,620 scientists use high-precision instruments 96 00:05:34,690 --> 00:05:37,660 to measure their radioactive properties. 97 00:05:37,730 --> 00:05:40,890 But why must scientists rely on meteorites 98 00:05:40,960 --> 00:05:44,360 to figure out how old the Earth really is? 99 00:05:44,430 --> 00:05:47,730 Why don't they simply study the oldest rocks 100 00:05:47,800 --> 00:05:50,170 that were formed on the Earth itself? 101 00:05:52,370 --> 00:05:55,410 From the Earth's formation around 4.6 billion years ago 102 00:05:55,480 --> 00:05:57,380 up to about 3.8 billion years ago, 103 00:05:57,450 --> 00:05:59,550 is an era called the hadean, 104 00:05:59,610 --> 00:06:02,850 when the Earth was undergoing heavy bombardment, 105 00:06:02,920 --> 00:06:05,120 and there's virtually no rock record 106 00:06:05,190 --> 00:06:09,720 from that period of time at all on the Earth remaining today. 107 00:06:13,460 --> 00:06:15,200 The hadean era, 108 00:06:15,260 --> 00:06:19,130 Greek for underworld, or hell. 109 00:06:19,200 --> 00:06:21,470 Nothing survived this inferno... 110 00:06:21,540 --> 00:06:23,100 Or did it? 111 00:06:23,170 --> 00:06:26,440 It was a missing link hundreds of millions of years long 112 00:06:26,510 --> 00:06:29,610 between Earth's creation and its oldest rocks, 113 00:06:29,680 --> 00:06:34,210 like these 3.6 billion-year-old rocks found in Australia. 114 00:06:34,280 --> 00:06:35,280 Beautiful. 115 00:06:37,090 --> 00:06:39,350 But breakthroughs in analyzing these rocks 116 00:06:39,420 --> 00:06:44,460 finally opened a window into the hadean. 117 00:06:44,530 --> 00:06:48,830 Interestingly, we do have some materials from that time. 118 00:06:48,900 --> 00:06:54,000 They are small zircon grains, 4.4 billion or so of age. 119 00:06:56,610 --> 00:06:58,740 Zircons are the oldest terrestrial material 120 00:06:58,810 --> 00:07:01,980 ever found on Earth. 121 00:07:02,040 --> 00:07:06,050 But rocks containing zircons that are billions of years old 122 00:07:06,110 --> 00:07:09,380 have only been discovered in a handful of places on Earth, 123 00:07:09,450 --> 00:07:11,480 like Antarctica. 124 00:07:11,550 --> 00:07:15,920 The rest have been obliterated. 125 00:07:15,990 --> 00:07:19,830 Studying those rare vestiges of the early days of Earth, 126 00:07:19,900 --> 00:07:22,630 scientists were astonished to find evidence 127 00:07:22,700 --> 00:07:26,070 that very early on, Earth developed a characteristic 128 00:07:26,130 --> 00:07:30,640 that it and no other planet in the solar system possesses: 129 00:07:30,710 --> 00:07:35,410 Plate tectonics. 130 00:07:35,480 --> 00:07:37,380 Plate tectonics has been around on Earth 131 00:07:37,450 --> 00:07:39,010 from the early days, 132 00:07:39,080 --> 00:07:42,280 at least 2 1/2, 3 billion years ago. 133 00:07:42,350 --> 00:07:45,080 So more than 3/4 of the life of the planet. 134 00:07:45,150 --> 00:07:49,160 Mars nearly developed plate tectonics, 135 00:07:49,220 --> 00:07:51,190 but failed. 136 00:07:51,260 --> 00:07:52,530 Mars is smaller than Earth. 137 00:07:52,590 --> 00:07:53,990 It cooled faster. 138 00:07:54,060 --> 00:07:56,160 It may well have had a style of plate tectonics 139 00:07:56,230 --> 00:08:01,100 early in its history, but it clearly does not today. 140 00:08:01,170 --> 00:08:04,000 Venus, considered Earth's sister planet, 141 00:08:04,070 --> 00:08:08,110 is also missing Earth's trait of plate tectonics. 142 00:08:08,180 --> 00:08:11,080 Venus doesn't have plate tectonics 143 00:08:11,150 --> 00:08:13,010 in the style that we recognize 144 00:08:13,080 --> 00:08:16,080 with very clear, linear boundaries between rigid plates, 145 00:08:16,150 --> 00:08:19,920 perhaps because there's no water on the surface of Venus. 146 00:08:27,460 --> 00:08:30,560 It is the striking and distinguishing characteristic 147 00:08:30,630 --> 00:08:33,500 of Earth's surface, 148 00:08:33,570 --> 00:08:37,100 and scientists are finding that this substance is the key 149 00:08:37,170 --> 00:08:39,310 that started Earth's early crust 150 00:08:39,370 --> 00:08:42,540 into constant, ever-changing motion. 151 00:08:44,210 --> 00:08:46,880 One of the reasons we have plate tectonics, 152 00:08:46,950 --> 00:08:48,550 which we don't see on any other planets, 153 00:08:48,580 --> 00:08:51,620 is that we have a lot of water on the Earth. 154 00:08:51,690 --> 00:08:54,320 So we have water not only in the oceans, 155 00:08:54,390 --> 00:08:56,820 but there's approximately an ocean's worth of water 156 00:08:56,890 --> 00:09:00,060 locked up in the rocks in, say, the upper 100 kilometers 157 00:09:00,130 --> 00:09:01,130 of the Earth. 158 00:09:03,100 --> 00:09:05,060 When you put water into a rock, 159 00:09:05,130 --> 00:09:08,030 it makes the rock weaker by maybe a factor of 100 160 00:09:08,100 --> 00:09:12,440 than it would be without the water. 161 00:09:12,510 --> 00:09:14,410 Weaker rocks make for plate tectonics 162 00:09:14,480 --> 00:09:16,940 because you have to have plate boundaries 163 00:09:17,010 --> 00:09:19,080 where rocks either slide by each other, 164 00:09:19,150 --> 00:09:22,720 or one goes down underneath the other. 165 00:09:22,780 --> 00:09:24,850 And so unless you have rocks that are weak enough 166 00:09:24,920 --> 00:09:27,250 to be able to slide past each other, 167 00:09:27,320 --> 00:09:29,020 you're not gonna have plate tectonics. 168 00:09:35,100 --> 00:09:37,200 But where did Earth's vast amount 169 00:09:37,270 --> 00:09:40,670 of liquid water come from? 170 00:09:40,740 --> 00:09:43,770 In the early history of the Earth, 171 00:09:43,840 --> 00:09:46,610 when there was a lot of volcanism going on, 172 00:09:46,680 --> 00:09:50,680 volcanoes actually brought gases up 173 00:09:50,750 --> 00:09:54,080 that created the early atmosphere. 174 00:09:54,150 --> 00:09:59,120 And magma has water in the form of vapor 175 00:09:59,190 --> 00:10:00,890 that it can bring up. 176 00:10:06,630 --> 00:10:08,390 Icy meteorites and comets 177 00:10:08,460 --> 00:10:10,300 were the other likely source 178 00:10:10,370 --> 00:10:12,800 that infused Earth's crust with water 179 00:10:12,870 --> 00:10:15,970 and got it moving. 180 00:10:16,040 --> 00:10:18,370 And once plate tectonics started, 181 00:10:18,440 --> 00:10:20,370 it never stopped. 182 00:10:20,440 --> 00:10:23,980 It has influenced everything that has happened on the surface 183 00:10:24,050 --> 00:10:25,310 including life. 184 00:10:29,350 --> 00:10:32,390 The oxygen, the minerals, everything that we get 185 00:10:32,450 --> 00:10:34,250 comes from the interior of the Earth. 186 00:10:36,990 --> 00:10:39,560 We all have internally within US 187 00:10:39,630 --> 00:10:42,300 a whole suite of minerals and things that... 188 00:10:42,360 --> 00:10:43,600 We're from the Earth. 189 00:10:43,670 --> 00:10:47,830 Essentially, that's where we... 190 00:10:47,900 --> 00:10:49,420 Our chemical makeup is from the Earth. 191 00:10:52,070 --> 00:10:55,910 And if you had no way of getting that outside of the Earth, 192 00:10:55,980 --> 00:10:58,380 then essentially you'd have a dead planet. 193 00:11:02,280 --> 00:11:04,380 Plate tectonics became recognized 194 00:11:04,450 --> 00:11:06,720 as being a crucial ingredient for life, 195 00:11:06,790 --> 00:11:10,090 as is water. 196 00:11:10,160 --> 00:11:11,790 This was an important piece of knowledge 197 00:11:11,860 --> 00:11:16,730 for scientists who were studying Earth's ancient rocks. 198 00:11:16,800 --> 00:11:19,400 If the conditions for life were present 199 00:11:19,470 --> 00:11:23,970 when Earth's ancient rocks formed billions of years ago, 200 00:11:24,040 --> 00:11:26,940 then wasn't it possible that life also took hold 201 00:11:27,010 --> 00:11:31,310 in the early dawn of Earth's formation? 202 00:11:31,380 --> 00:11:33,210 The search was on. 203 00:11:35,820 --> 00:11:40,550 Some scientists zeroed in on the 3.5 billion-year-old rocks 204 00:11:40,620 --> 00:11:44,020 in the outback of western Australia. 205 00:11:44,090 --> 00:11:48,460 Amazingly, it turns out that fairly soon after, 206 00:11:48,530 --> 00:11:51,600 people started discovering some potential signs of life 207 00:11:51,670 --> 00:11:52,970 in those rocks, 208 00:11:53,030 --> 00:11:55,500 and one of the major discoveries 209 00:11:55,570 --> 00:11:57,070 was structures called stromatolites. 210 00:12:01,380 --> 00:12:04,010 Stromatolites are peculiar rocky structures 211 00:12:04,080 --> 00:12:06,380 built by colonies of cyanobacteria, 212 00:12:06,450 --> 00:12:09,650 or blue-green algae. 213 00:12:09,720 --> 00:12:12,120 They are extremely rare on Earth today, 214 00:12:12,190 --> 00:12:14,350 growing in only a few places, 215 00:12:14,420 --> 00:12:18,260 like laguna Bacalar in Mexico. 216 00:12:18,330 --> 00:12:21,830 But they were the first life forms to appear on Earth, 217 00:12:21,900 --> 00:12:24,800 and they gave rise to all other forms of life, 218 00:12:24,870 --> 00:12:27,200 including people. 219 00:12:27,270 --> 00:12:30,040 It took awhile, though. 220 00:12:30,100 --> 00:12:32,310 Stromatolites dominate the first 3 billion years 221 00:12:32,370 --> 00:12:34,210 of the history of life on Earth. 222 00:12:34,280 --> 00:12:37,440 So from 3 1/2 billion years ago 223 00:12:37,510 --> 00:12:38,990 to up to about 1/2 a billion years ago, 224 00:12:39,010 --> 00:12:41,410 the fossil record consists 225 00:12:41,480 --> 00:12:43,420 almost entirely of stromatolites. 226 00:12:47,160 --> 00:12:50,760 Stromatolites lived in oceans and lakes. 227 00:12:50,830 --> 00:12:53,690 For that period, no fossils have been found 228 00:12:53,760 --> 00:12:56,000 of creatures that lived on land. 229 00:12:56,060 --> 00:12:58,900 Does that mean there were no continents 230 00:12:58,970 --> 00:13:03,000 for the first 3 billion years of Earth's history? 231 00:13:03,070 --> 00:13:04,470 Once again, 232 00:13:04,540 --> 00:13:09,340 Earth's ancient rocks yielded clues to this mystery. 233 00:13:09,410 --> 00:13:11,530 We don't know for sure when plate tectonics started, 234 00:13:11,580 --> 00:13:16,680 but we do know for sure when we first had continents. 235 00:13:16,750 --> 00:13:19,720 We have intact areas that we can go and map in 236 00:13:19,790 --> 00:13:22,690 that go back as far as 4 billion years. 237 00:13:22,760 --> 00:13:26,160 That's nearly 90% of the age of the Earth, 238 00:13:26,230 --> 00:13:28,560 so we're quite sure about the fact 239 00:13:28,630 --> 00:13:30,560 that we had continents back that far. 240 00:13:34,040 --> 00:13:36,040 No one knows what the continents were like 241 00:13:36,100 --> 00:13:38,540 4 billion years ago 242 00:13:38,610 --> 00:13:40,640 or why we ended up with seven continents 243 00:13:40,710 --> 00:13:44,010 that ride around on a dozen large crustal plates 244 00:13:44,080 --> 00:13:47,850 and many microplates in between. 245 00:13:47,920 --> 00:13:53,750 But the question that plagued scientists for years was this: 246 00:13:53,820 --> 00:13:57,320 What was the prime force that made the plates move? 247 00:14:02,230 --> 00:14:05,030 There were two contending forces. 248 00:14:05,100 --> 00:14:09,200 The first was discovered aboard seafaring research vessels 249 00:14:09,270 --> 00:14:13,540 mapping the sea floor decades ago. 250 00:14:13,610 --> 00:14:15,510 Scientists learned that the sea floor 251 00:14:15,580 --> 00:14:18,440 was spreading apart in the middle of the oceans 252 00:14:18,510 --> 00:14:22,680 at submarine mountain ranges called mid-ocean ridges. 253 00:14:22,750 --> 00:14:25,020 Submersibles were sent down 254 00:14:25,090 --> 00:14:27,850 and came back with footage of hot gases welling up 255 00:14:27,920 --> 00:14:30,890 in the rift zones. 256 00:14:30,960 --> 00:14:33,230 Magma was rising from below here, 257 00:14:33,290 --> 00:14:35,230 and it was believed that it was pushing 258 00:14:35,300 --> 00:14:39,370 the oceanic plates apart. 259 00:14:39,430 --> 00:14:43,900 The key to plate tectonics was at last discovered... 260 00:14:43,970 --> 00:14:47,370 Or was it? 261 00:14:47,440 --> 00:14:51,110 Seismic experiments of Earth's deep crust and mantle 262 00:14:51,180 --> 00:14:53,910 changed scientists' thinking. 263 00:14:53,980 --> 00:14:56,680 A second force was discovered 264 00:14:56,750 --> 00:14:59,020 where plates collided head-on, 265 00:14:59,090 --> 00:15:02,720 as they do under the Andes mountains of Ecuador. 266 00:15:02,790 --> 00:15:06,730 One plate was imaged diving underneath the other. 267 00:15:06,790 --> 00:15:10,330 The was called a subduction zone. 268 00:15:10,400 --> 00:15:13,000 The sinking slab appeared to be pulling 269 00:15:13,070 --> 00:15:14,970 the rest of the plate behind it, 270 00:15:15,040 --> 00:15:18,400 making the entire plate move. 271 00:15:18,470 --> 00:15:22,040 A great debate arose over which force was more important 272 00:15:22,110 --> 00:15:25,010 in driving plate tectonics: 273 00:15:25,080 --> 00:15:30,920 Pushing from the rising magma or pulling in subduction zones. 274 00:15:30,990 --> 00:15:34,920 There now appears to be a winner. 275 00:15:34,990 --> 00:15:38,260 When people first recognized mid-ocean ridge spreading 276 00:15:38,330 --> 00:15:40,860 as the key to understanding plate tectonics, 277 00:15:40,930 --> 00:15:45,300 the view was that the magma, the mantle, 278 00:15:45,370 --> 00:15:49,370 rose up in the center and forced the plates apart. 279 00:15:49,440 --> 00:15:51,740 But that view has changed over the years 280 00:15:51,810 --> 00:15:55,440 and has largely been replaced by the view that it's the pull 281 00:15:55,510 --> 00:15:58,310 of the subduction slab that matters most. 282 00:15:58,380 --> 00:16:01,950 Bob, can you please hand me the pvc pipe, please? 283 00:16:02,020 --> 00:16:04,350 Sure. 284 00:16:04,420 --> 00:16:07,190 So scientists looked harder at subduction, 285 00:16:07,260 --> 00:16:13,260 and as they did, more geologic wonders were uncovered. 286 00:16:13,330 --> 00:16:17,100 For one, seismic studies of subduction zones 287 00:16:17,170 --> 00:16:19,670 revealed that oceanic plates are very thin 288 00:16:19,730 --> 00:16:22,330 compared to continents. 289 00:16:22,400 --> 00:16:25,910 The sea floor is 3 to 6 miles thick, 290 00:16:25,970 --> 00:16:28,810 while continents average 30 miles thick 291 00:16:28,880 --> 00:16:33,610 and swell up to 50 miles under great mountain belts. 292 00:16:33,680 --> 00:16:35,680 This has a major influence 293 00:16:35,750 --> 00:16:38,250 on how the plates affect each other, 294 00:16:38,320 --> 00:16:41,390 especially in subduction zones. 295 00:16:41,460 --> 00:16:44,390 Where subducting plates meet continents, 296 00:16:44,460 --> 00:16:47,230 Earth's tallest mountains are built: 297 00:16:47,300 --> 00:16:50,360 The Himalaya of Asia, 298 00:16:50,430 --> 00:16:52,730 the Alps of Europe, 299 00:16:52,800 --> 00:16:55,430 the Andes of South America. 300 00:16:55,500 --> 00:16:58,100 Subduction created them all. 301 00:17:00,240 --> 00:17:05,010 But subduction can create havoc on the surface. 302 00:17:05,080 --> 00:17:08,080 As seismic networks improved around the world, 303 00:17:08,150 --> 00:17:11,050 it became apparent that subduction was the culprit 304 00:17:11,120 --> 00:17:14,350 behind Earth's most powerful earthquakes. 305 00:17:16,820 --> 00:17:20,430 First the earthquake itself... 306 00:17:22,400 --> 00:17:25,760 A grocery store in the capital at the moment of impact. 307 00:17:25,830 --> 00:17:28,300 The tohoku earthquake of 2011 308 00:17:28,370 --> 00:17:30,870 was the most powerful ever known in Japan 309 00:17:30,940 --> 00:17:34,510 at magnitude 9. 310 00:17:34,580 --> 00:17:36,880 It struck where the oceanic pacific plate 311 00:17:36,940 --> 00:17:40,580 subducts under a piece of the north American plate. 312 00:17:43,020 --> 00:17:45,050 Where subduction is occurring, 313 00:17:45,120 --> 00:17:49,990 you see a very well-defined zone of earthquakes, 314 00:17:50,060 --> 00:17:53,860 essentially between the downgoing oceanic crust 315 00:17:53,930 --> 00:17:58,160 and the continental crust, 316 00:17:58,230 --> 00:18:00,470 and it forms a line of earthquakes 317 00:18:00,540 --> 00:18:04,040 where these two crusts are in contact with each other 318 00:18:04,110 --> 00:18:08,940 and slipping past each other. 319 00:18:12,310 --> 00:18:14,150 Subduction quakes can also generate 320 00:18:14,220 --> 00:18:15,980 devastating tsunamis 321 00:18:16,050 --> 00:18:18,520 because of their proximity to coastlines. 322 00:18:18,590 --> 00:18:20,820 One of the worst earthquakes ever... 323 00:18:20,890 --> 00:18:24,490 The Japanese quake and the 2004 Indian ocean earthquake 324 00:18:24,560 --> 00:18:27,530 off sumatra are striking examples. 325 00:18:35,400 --> 00:18:38,140 Earthquakes and tsunamis are not the only action 326 00:18:38,210 --> 00:18:40,870 spawned by subduction. 327 00:18:40,940 --> 00:18:43,640 Subduction also creates volcanoes, 328 00:18:43,710 --> 00:18:48,410 and they, too, can be large and dangerous. 329 00:18:48,480 --> 00:18:52,220 Volcanoes in the subduction zones are formed 330 00:18:52,290 --> 00:18:57,920 by magmas that are more silicic, or more viscous, 331 00:18:57,990 --> 00:19:01,690 and they are much more explosive. 332 00:19:01,760 --> 00:19:05,160 So those are the volcanoes that can really be dangerous 333 00:19:05,230 --> 00:19:07,230 and really create trouble. 334 00:19:11,710 --> 00:19:15,910 Subduction volcanoes are Earth's most notorious: 335 00:19:15,980 --> 00:19:19,510 Mount Tungurahua in Ecuador, 336 00:19:19,580 --> 00:19:23,020 mount Vesuvius in Italy, 337 00:19:23,080 --> 00:19:25,820 mount Asama in Japan, 338 00:19:25,890 --> 00:19:28,720 mount Saint Helens in the u.S. 339 00:19:28,790 --> 00:19:32,630 All are known for explosive, destructive eruptions. 340 00:19:34,130 --> 00:19:37,060 They also grow to great heights. 341 00:19:37,130 --> 00:19:38,960 This is chimborazo, 342 00:19:39,030 --> 00:19:42,200 rising 20,700 feet above sea level 343 00:19:42,270 --> 00:19:45,970 in the Andes mountains of Ecuador. 344 00:19:46,040 --> 00:19:48,140 When measured from the center of the Earth's core 345 00:19:48,210 --> 00:19:50,010 to the volcano's summit, 346 00:19:50,080 --> 00:19:53,080 chimborazo is Earth's tallest mountain, 347 00:19:53,150 --> 00:19:57,380 soaring over 7,000 feet closer to the sun than mount Everest. 348 00:19:59,150 --> 00:20:02,250 That's because the volcano sits on the equator 349 00:20:02,320 --> 00:20:05,590 where the Earth bulges outward from the force of rotation. 350 00:20:10,970 --> 00:20:13,170 Earth scientists have gotten a good handle 351 00:20:13,230 --> 00:20:15,270 on the forces driving plate tectonics, 352 00:20:15,340 --> 00:20:17,800 like subduction, 353 00:20:17,870 --> 00:20:20,470 but questions remain. 354 00:20:20,540 --> 00:20:24,540 One of the biggest questions is how plate tectonics is linked 355 00:20:24,610 --> 00:20:27,980 to processes operating deep below Earth's crust. 356 00:20:30,450 --> 00:20:34,090 The deeper we look, the less we know. 357 00:20:34,160 --> 00:20:36,990 But new research is turning up big surprises 358 00:20:37,060 --> 00:20:39,860 lurking in the center of the Earth. 359 00:20:39,930 --> 00:20:41,960 Tumble into cascading salt beds, 360 00:20:42,030 --> 00:20:45,360 escape from hissing steam caves, 361 00:20:45,430 --> 00:20:49,030 behold the staggering underground ocean. 362 00:20:49,100 --> 00:20:52,140 You will encounter breathtaking dangers beyond belief 363 00:20:52,210 --> 00:20:54,770 here at the center of the Earth. 364 00:20:56,740 --> 00:20:58,580 The inside of Earth, 365 00:20:58,650 --> 00:21:01,080 an object of great curiosity, 366 00:21:01,150 --> 00:21:03,920 wild conjecture. 367 00:21:03,980 --> 00:21:06,690 At the center of it all is the Earth's core, 368 00:21:06,750 --> 00:21:12,490 which was discovered accidentally only 140 years ago. 369 00:21:12,560 --> 00:21:15,430 A huge earthquake in the 1880s was... 370 00:21:15,500 --> 00:21:17,100 The waves from that earthquake, 371 00:21:17,160 --> 00:21:18,660 traveling through the Earth's core, 372 00:21:18,730 --> 00:21:21,000 bouncing off the Earth's core, 373 00:21:21,070 --> 00:21:23,900 were recognized as arriving at different times 374 00:21:23,970 --> 00:21:25,500 from the seismic waves 375 00:21:25,570 --> 00:21:27,710 that traveled through the outer layers of the Earth. 376 00:21:27,780 --> 00:21:30,580 And with that, the Earth's core was discovered. 377 00:21:30,640 --> 00:21:33,150 It took until the 1920s to recognize 378 00:21:33,210 --> 00:21:35,710 that the Earth had a solid inner core 379 00:21:35,780 --> 00:21:39,250 inside the fluid outer core. 380 00:21:39,320 --> 00:21:41,690 At half the size of the planet, 381 00:21:41,760 --> 00:21:47,330 the Earth's core is peculiar in that it's all made of iron. 382 00:21:47,400 --> 00:21:52,300 But its inner half is solid, and its outer half is liquid. 383 00:21:52,370 --> 00:21:54,800 The Earth's outer core is molten 384 00:21:54,870 --> 00:21:57,040 because it's very high temperature, and it's... 385 00:21:57,100 --> 00:21:58,820 The temperatures are above the melting temperature 386 00:21:58,840 --> 00:22:00,310 of this iron-rich material, 387 00:22:00,370 --> 00:22:02,540 but the Earth's inner core is actually... can be solid 388 00:22:02,610 --> 00:22:05,380 because we have even higher pressures, 389 00:22:05,450 --> 00:22:07,880 so get to over 3 million atmospheres, 390 00:22:07,950 --> 00:22:11,020 so 3 million times the pressure at the surface of the planet. 391 00:22:11,090 --> 00:22:12,580 And at those high pressures, 392 00:22:12,650 --> 00:22:14,890 they cause the material to actually solidify. 393 00:22:18,430 --> 00:22:21,360 Fortunately for US and all living things, 394 00:22:21,430 --> 00:22:23,830 the Earth's outer core is fluid, 395 00:22:23,900 --> 00:22:28,730 for it generates our planet's protective magnetic field. 396 00:22:28,800 --> 00:22:31,270 If we didn't have the Earth's magnetic field today, 397 00:22:31,340 --> 00:22:34,910 we probably couldn't have life on the surface of the planet. 398 00:22:34,980 --> 00:22:37,780 The sun's always throwing all these particles at the planet, 399 00:22:37,850 --> 00:22:39,340 but then the Earth's magnetic field 400 00:22:39,410 --> 00:22:41,310 protects this nice, protective coating 401 00:22:41,380 --> 00:22:43,880 that protects US from these damaging rays 402 00:22:43,950 --> 00:22:45,880 and particle... High-energy particles. 403 00:22:48,390 --> 00:22:50,060 The Earth is unique among planets 404 00:22:50,120 --> 00:22:52,860 in having a magnetic field. 405 00:22:52,930 --> 00:22:54,890 Mars had one early on, 406 00:22:54,960 --> 00:22:56,900 but its small core cooled quickly, 407 00:22:56,960 --> 00:22:59,900 and it was lost and, with it, 408 00:22:59,970 --> 00:23:03,470 the chance for life to take hold on its surface. 409 00:23:03,540 --> 00:23:07,570 Meanwhile, Earth's magnetic field, for all its importance, 410 00:23:07,640 --> 00:23:11,280 is not well understood. 411 00:23:11,350 --> 00:23:14,350 What is getting clearer is what is actually going on 412 00:23:14,420 --> 00:23:16,450 in the Earth's core itself. 413 00:23:16,520 --> 00:23:18,350 Okay. Let's put it on there. 414 00:23:18,420 --> 00:23:19,650 That is because 415 00:23:19,720 --> 00:23:21,150 scientists have finally re-created 416 00:23:21,220 --> 00:23:24,690 the core's extreme conditions in the lab. 417 00:23:24,760 --> 00:23:28,760 3 million atmospheres and 10,000 degrees fahrenheit, 418 00:23:28,830 --> 00:23:31,960 the same temperature as the surface of the sun. 419 00:23:35,140 --> 00:23:37,270 So you have to reach millions of atmospheres, 420 00:23:37,340 --> 00:23:39,020 and you have to reach thousands of degrees, 421 00:23:39,040 --> 00:23:42,040 so that's a very challenging technological problem. 422 00:23:42,110 --> 00:23:43,040 Okay, great. 423 00:23:43,110 --> 00:23:45,940 Looks good. 424 00:23:46,010 --> 00:23:48,310 So one way to reach the very high pressures 425 00:23:48,380 --> 00:23:51,050 and temperatures in the planet is to compress materials 426 00:23:51,120 --> 00:23:52,920 between the tips of two diamonds, 427 00:23:52,990 --> 00:23:56,220 and since diamond is the hardest material on the planet, 428 00:23:56,290 --> 00:24:00,190 we can generate very high pressures. 429 00:24:00,260 --> 00:24:01,590 And then, at the same time, 430 00:24:01,660 --> 00:24:03,960 we can use lasers to heat the sample 431 00:24:04,030 --> 00:24:05,800 and to reach the same conditions 432 00:24:05,870 --> 00:24:09,970 we think are inside the planet. 433 00:24:10,040 --> 00:24:14,610 The core's sun-hot heat is crucial to understand. 434 00:24:14,680 --> 00:24:16,640 It affects everything at the surface, 435 00:24:16,710 --> 00:24:20,150 1,800 miles above. 436 00:24:20,210 --> 00:24:21,450 To get up here, 437 00:24:21,520 --> 00:24:25,520 it travels through two layers of solid rock. 438 00:24:25,590 --> 00:24:29,760 The first is the mantle, Earth's biggest layer by far. 439 00:24:31,360 --> 00:24:32,960 And then the crust, 440 00:24:33,030 --> 00:24:36,830 really just a thin veneer on the Earth. 441 00:24:36,900 --> 00:24:40,070 Scientists believe that the immense heat of the core 442 00:24:40,130 --> 00:24:43,270 makes the mantle so hot that it acts like a fluid 443 00:24:43,340 --> 00:24:46,610 and rises until it hits the crust. 444 00:24:46,670 --> 00:24:50,680 Some of the heat then circulates along the crust's underside 445 00:24:50,740 --> 00:24:54,950 until subducting slabs of crust take it downward. 446 00:24:55,020 --> 00:24:58,920 It's a giant recycling treadmill called convection. 447 00:25:00,920 --> 00:25:02,320 Through experiments, 448 00:25:02,390 --> 00:25:05,060 scientists have calculated that heat's round trip 449 00:25:05,130 --> 00:25:08,730 from the core to the crust and back to the core again 450 00:25:08,800 --> 00:25:12,500 takes 300 million years. 451 00:25:12,570 --> 00:25:15,030 This circulation of heat is kept alive 452 00:25:15,100 --> 00:25:17,040 by the sinking of cold, heavy plates 453 00:25:17,100 --> 00:25:19,770 into the hot mantle below. 454 00:25:19,840 --> 00:25:21,170 In other words, 455 00:25:21,240 --> 00:25:24,710 those slabs cause quite a stir as they descend. 456 00:25:26,680 --> 00:25:28,910 We can track those slabs with tomography 457 00:25:28,980 --> 00:25:31,480 down at least into the middle mantle. 458 00:25:31,550 --> 00:25:33,620 And probably those slabs reach all the way 459 00:25:33,690 --> 00:25:35,520 to the core-mantle boundary, 460 00:25:35,590 --> 00:25:39,990 and there's a slab graveyard that sits above the core. 461 00:25:40,060 --> 00:25:44,400 That slab graveyard may in turn help drive 462 00:25:44,470 --> 00:25:47,070 the convection cells in Earth's mantle 463 00:25:47,130 --> 00:25:49,170 that in turn then reach up 464 00:25:49,240 --> 00:25:51,470 and drive the pattern of plate tectonics 465 00:25:51,540 --> 00:25:53,340 and the shifting plates at Earth's surface. 466 00:25:55,440 --> 00:25:58,480 The sinking slabs not only drive heat in the mantle; 467 00:25:58,550 --> 00:26:01,480 they have radically changed the makeup of the mantle 468 00:26:01,550 --> 00:26:05,950 over the course of geologic time. 469 00:26:06,020 --> 00:26:10,160 The mantle is a very complicated mixture of things 470 00:26:10,220 --> 00:26:12,420 that have been stirred internally 471 00:26:12,490 --> 00:26:14,660 and things that have come up to the surface, 472 00:26:14,730 --> 00:26:18,460 been ocean floor for a while, and then taken back down. 473 00:26:20,830 --> 00:26:23,640 In the 4.5 billion-year history of the Earth, 474 00:26:23,700 --> 00:26:28,010 the entire mantle has been circulated about once. 475 00:26:28,080 --> 00:26:30,240 Virtually nothing at the Earth's surface 476 00:26:30,310 --> 00:26:32,540 or in the interior is permanent. 477 00:26:32,610 --> 00:26:33,930 Things are changing all the time. 478 00:26:38,450 --> 00:26:40,390 Heat rising up from the core 479 00:26:40,450 --> 00:26:43,620 does not always recycle back down. 480 00:26:43,690 --> 00:26:47,060 Sometimes it escapes its earthly confines 481 00:26:47,130 --> 00:26:52,000 as volcanic eruptions. 482 00:26:52,070 --> 00:26:53,770 Earth is by far 483 00:26:53,830 --> 00:26:58,540 the solar system's most volcanically active planet. 484 00:26:58,610 --> 00:27:03,410 Volcanoes are nature's most violent and destructive force. 485 00:27:03,480 --> 00:27:05,110 But ironically, 486 00:27:05,180 --> 00:27:08,850 this force emanating from the Earth's mantle deep below 487 00:27:08,920 --> 00:27:12,320 is at the very root of the creation and maintenance 488 00:27:12,390 --> 00:27:15,190 of life on Earth's surface. 489 00:27:16,960 --> 00:27:20,060 Volcanoes have certainly influenced life on Earth. 490 00:27:20,130 --> 00:27:23,130 And that's not just when they have a big eruption 491 00:27:23,200 --> 00:27:24,430 and people die. 492 00:27:24,500 --> 00:27:29,600 But they also may have created life on Earth. 493 00:27:29,670 --> 00:27:31,870 In the last few decades, 494 00:27:31,940 --> 00:27:35,510 hydrothermal vents were discovered deep in the ocean, 495 00:27:35,580 --> 00:27:39,780 and minerals are coming out that can actually feed life 496 00:27:39,850 --> 00:27:41,480 around those vents, 497 00:27:41,550 --> 00:27:45,380 and a very surprising find was that life could exist 498 00:27:45,450 --> 00:27:48,490 at such depth in the ocean. 499 00:27:52,630 --> 00:27:55,130 Volcanoes were the original architects 500 00:27:55,200 --> 00:27:56,930 of our atmosphere, 501 00:27:57,000 --> 00:27:59,930 unlocking co2 and water from the mantle's rocks 502 00:28:00,000 --> 00:28:02,000 and taking them to the surface. 503 00:28:04,070 --> 00:28:05,600 One of the largest concentrations 504 00:28:05,670 --> 00:28:09,110 of active volcanoes on Earth is in Japan... 505 00:28:09,180 --> 00:28:11,180 More than 100. 506 00:28:11,250 --> 00:28:14,710 Mount fuji is Japan's largest volcano, 507 00:28:14,780 --> 00:28:18,850 rising 12,400 feet high. 508 00:28:18,920 --> 00:28:22,950 This graceful peak is a massive subduction volcano, 509 00:28:23,020 --> 00:28:27,460 but the largest volcanoes on Earth are 100 times bigger. 510 00:28:29,200 --> 00:28:31,160 They belong to a rare class of volcano 511 00:28:31,230 --> 00:28:35,200 known as a mantle plume volcano, 512 00:28:35,270 --> 00:28:37,770 and the largest of all are on Hawaii. 513 00:28:41,070 --> 00:28:44,010 Lava has been erupting from this spot in the pacific 514 00:28:44,080 --> 00:28:48,110 for at least 75 million years. 515 00:28:48,180 --> 00:28:53,290 It built Mauna Loa, Earth's largest volcano by volume. 516 00:28:53,350 --> 00:28:59,090 But Mauna Loa is not the biggest volcano in the solar system. 517 00:28:59,160 --> 00:29:01,190 The largest volcano in the solar system 518 00:29:01,260 --> 00:29:05,130 is Olympus mons on Mars. 519 00:29:05,200 --> 00:29:08,000 It's about 26 kilometers high 520 00:29:08,070 --> 00:29:13,140 and around 600 kilometers across. 521 00:29:15,310 --> 00:29:16,810 Compared to Hawaii, 522 00:29:16,880 --> 00:29:21,350 Olympus mons is vastly bigger in all respects. 523 00:29:21,420 --> 00:29:25,920 Why are Earth's volcanoes so much smaller? 524 00:29:25,990 --> 00:29:28,390 On Mars, there's no plate tectonics, 525 00:29:28,460 --> 00:29:33,590 so the same, let's say, hot spot can build up a volcano 526 00:29:33,660 --> 00:29:37,600 in the same location for very, very long periods of time. 527 00:29:41,000 --> 00:29:43,100 On the Earth, we can't have that situation 528 00:29:43,170 --> 00:29:46,270 because the plates are moving, so you get, for example, 529 00:29:46,340 --> 00:29:50,410 hot spot like the one that formed the Hawaiian volcanoes, 530 00:29:50,480 --> 00:29:54,580 but the plate is moving over it, so it punches one volcano, 531 00:29:54,650 --> 00:29:56,010 but then the plate moves, 532 00:29:56,080 --> 00:30:00,420 and the volcano moves somewhere else. 533 00:30:00,490 --> 00:30:05,160 So on Earth, we don't really build those sizes of volcanoes. 534 00:30:09,730 --> 00:30:12,600 The source that feeds Earth's giant volcanoes 535 00:30:12,670 --> 00:30:15,200 is thought to be a narrow cylinder of hot rock 536 00:30:15,270 --> 00:30:18,240 that reaches deep into the mantle. 537 00:30:18,310 --> 00:30:21,170 How deep is a matter of debate. 538 00:30:21,240 --> 00:30:23,740 But recent seismic studies of the Hawaiian chain 539 00:30:23,810 --> 00:30:26,040 imaged for the first time 540 00:30:26,110 --> 00:30:29,310 a hot plume reaching halfway to the Earth's core. 541 00:30:31,450 --> 00:30:34,850 Chemical analysis of lavas retrieved in drill cores 542 00:30:34,920 --> 00:30:37,490 traces the plume even deeper, 543 00:30:37,560 --> 00:30:40,960 actually extending to the Earth's core itself. 544 00:30:43,860 --> 00:30:46,430 The deepest reaches of our planet, then, 545 00:30:46,500 --> 00:30:48,030 are intimately connected 546 00:30:48,100 --> 00:30:51,270 with geological action at the surface. 547 00:30:54,340 --> 00:30:56,410 Without these deep-seated forces, 548 00:30:56,480 --> 00:31:01,910 life would have not gained a foothold on our planet, 549 00:31:01,980 --> 00:31:03,380 and it wouldn't have flourished 550 00:31:03,450 --> 00:31:06,580 and evolved into countless wondrous forms 551 00:31:06,650 --> 00:31:09,590 without something else: 552 00:31:09,660 --> 00:31:13,020 A remarkably stable, precisely tuned climate. 553 00:31:18,870 --> 00:31:21,300 For most of Earth's existence, 554 00:31:21,370 --> 00:31:23,900 the temperature at the surface has rarely wavered. 555 00:31:25,770 --> 00:31:29,170 Why this is is a great mystery. 556 00:31:29,240 --> 00:31:34,010 The global mean temperature is a comfortable 59 degrees. 557 00:31:34,080 --> 00:31:36,350 Increase that by just 18 degrees, 558 00:31:36,420 --> 00:31:40,790 and ice at the Poles would melt. 559 00:31:40,850 --> 00:31:43,250 Decrease it by 18 degrees, 560 00:31:43,320 --> 00:31:46,060 and the entire world would freeze over. 561 00:31:47,760 --> 00:31:50,860 Other planets are far from habitable. 562 00:31:50,930 --> 00:31:54,270 Venus, with 200,000 times more co2 563 00:31:54,330 --> 00:31:56,200 in its atmosphere than Earth, 564 00:31:56,270 --> 00:32:00,270 is ravaged by temperatures reaching 900 degrees fahrenheit. 565 00:32:03,010 --> 00:32:07,050 Mars, long ago stripped of its atmosphere and magnetic shield, 566 00:32:07,110 --> 00:32:12,280 is deeply frozen to an average of 70 degrees below zero. 567 00:32:19,830 --> 00:32:23,160 Earth's climate is kept moderate by a little understood interplay 568 00:32:23,230 --> 00:32:27,500 of geologic and biologic forces. 569 00:32:27,570 --> 00:32:31,300 Volcanic eruptions spew co2 into the air. 570 00:32:31,370 --> 00:32:34,270 Plate tectonics builds mountains 571 00:32:34,340 --> 00:32:37,810 and rifts apart ocean basins. 572 00:32:37,880 --> 00:32:40,350 Then weather erodes the land, 573 00:32:40,410 --> 00:32:42,110 capturing CO2 574 00:32:42,180 --> 00:32:45,320 and locking it away in sediments. 575 00:32:45,390 --> 00:32:49,950 Living organisms add their alterations into the mix. 576 00:32:50,020 --> 00:32:53,930 All is built into a system of global checks and balances. 577 00:32:58,000 --> 00:32:59,700 There have been only a few times 578 00:32:59,770 --> 00:33:03,900 when Earth's climate tipped well beyond its comfort zone. 579 00:33:03,970 --> 00:33:09,410 Earth's coldest extreme happened about 750 million years ago 580 00:33:09,480 --> 00:33:13,080 and probably several times before that. 581 00:33:13,150 --> 00:33:17,180 It was called snowball Earth. 582 00:33:17,250 --> 00:33:19,850 Snowball Earth refers to a time in the Earth's history 583 00:33:19,920 --> 00:33:23,290 when the Earth was entirely covered with ice. 584 00:33:23,360 --> 00:33:25,960 That means glaciers on the continents 585 00:33:26,030 --> 00:33:28,290 and sea ice covering most of the oceans 586 00:33:28,360 --> 00:33:31,760 all the way down to the equator. 587 00:33:31,830 --> 00:33:33,470 During snowball Earth, 588 00:33:33,530 --> 00:33:35,400 the temperature at the equator plunged 589 00:33:35,470 --> 00:33:38,300 to minus 4 degrees fahrenheit. 590 00:33:38,370 --> 00:33:41,240 Life, still in its primitive bacterial stage, 591 00:33:41,310 --> 00:33:44,810 survived the deep freeze as it does today: 592 00:33:44,880 --> 00:33:47,980 Below ice shelves and even below glaciers. 593 00:33:50,680 --> 00:33:53,820 Scientists think that the trigger for snowball Earth 594 00:33:53,890 --> 00:33:59,160 was the bunching of continents at the equator. 595 00:33:59,230 --> 00:34:01,690 The giant land mass attracted moisture, 596 00:34:01,760 --> 00:34:04,700 and great storms ensued. 597 00:34:04,760 --> 00:34:07,870 Rain stripped co2 from the atmosphere 598 00:34:07,930 --> 00:34:12,340 and locked it in eroding sediments. 599 00:34:12,410 --> 00:34:15,710 As co2 levels dropped, so did the temperature. 600 00:34:22,020 --> 00:34:25,820 Volcanic eruptions eventually overpowered snowball Earth 601 00:34:25,890 --> 00:34:30,520 by injecting co2 back into the atmosphere. 602 00:34:30,590 --> 00:34:32,420 As the climate restabilized, 603 00:34:32,490 --> 00:34:36,030 the surviving bacterial life forms multiplied, 604 00:34:36,100 --> 00:34:37,760 photosynthesized, 605 00:34:37,830 --> 00:34:40,130 and filled the air with oxygen, 606 00:34:40,200 --> 00:34:43,170 a requirement for more complex life. 607 00:34:44,840 --> 00:34:48,810 Finally, 550 million years ago, 608 00:34:48,880 --> 00:34:51,810 life branched out and began its extraordinary journey 609 00:34:51,880 --> 00:34:54,810 of diversification and evolution. 610 00:34:57,820 --> 00:35:01,450 Why this happened is still a mystery, 611 00:35:01,520 --> 00:35:04,060 but the extreme hit that life took 612 00:35:04,120 --> 00:35:05,590 during snowball Earth 613 00:35:05,660 --> 00:35:10,200 may have actually been part of the reason. 614 00:35:10,260 --> 00:35:12,100 Once life was established on the Earth, 615 00:35:12,170 --> 00:35:15,100 it continued to show evidence that it was extremely adaptable, 616 00:35:15,170 --> 00:35:18,500 that whatever harsh conditions were thrown at it, 617 00:35:18,570 --> 00:35:22,710 that it was able to adapt to find a way to survive. 618 00:35:22,780 --> 00:35:25,580 So even through periods like snowball Earth, 619 00:35:25,650 --> 00:35:28,680 life would adapt to those conditions and reemerge. 620 00:35:28,750 --> 00:35:31,920 And in fact, those sorts of conditions were major factors 621 00:35:31,990 --> 00:35:33,950 driving the evolution of life on Earth. 622 00:35:38,330 --> 00:35:41,490 The next time Earth's climate was knocked off balance 623 00:35:41,560 --> 00:35:45,130 was at a time when Earth experienced its biggest upheaval 624 00:35:45,200 --> 00:35:48,870 since the early days of its formation. 625 00:35:48,940 --> 00:35:52,000 About 250 million years ago, 626 00:35:52,070 --> 00:35:55,310 95% of life on Earth disappeared. 627 00:35:57,940 --> 00:36:00,610 We think that's because of very large eruptions 628 00:36:00,680 --> 00:36:03,820 in the siberian traps. 629 00:36:07,190 --> 00:36:11,160 Earth scientists have mapped 800,000 square miles 630 00:36:11,220 --> 00:36:14,090 of Siberia that were covered by lava flows 631 00:36:14,160 --> 00:36:17,560 up to 12,000 feet thick. 632 00:36:17,630 --> 00:36:21,630 They call this province the siberian traps. 633 00:36:21,700 --> 00:36:25,000 Those eruptions would have put a lot of dust, 634 00:36:25,070 --> 00:36:28,170 a lot of sulfur in the atmosphere, 635 00:36:28,240 --> 00:36:30,810 cooled the temperature. 636 00:36:30,880 --> 00:36:34,950 So this killed a lot of life on Earth. 637 00:36:35,020 --> 00:36:39,480 The climate recovered eventually, and so did life. 638 00:36:39,550 --> 00:36:41,050 But 90 million years ago, 639 00:36:41,120 --> 00:36:45,690 the hottest period ever known enveloped the Earth. 640 00:36:45,760 --> 00:36:49,130 Dinosaurs roamed what are now the icy realms 641 00:36:49,200 --> 00:36:51,130 of the arctic circle. 642 00:36:51,200 --> 00:36:56,270 Around them were fellow swamp-dwellers like alligators. 643 00:36:56,340 --> 00:37:00,100 What were they doing at the Earth's Poles? 644 00:37:00,170 --> 00:37:04,280 Scientists figured out that plate tectonics was the culprit. 645 00:37:05,750 --> 00:37:07,510 100 million years ago, 646 00:37:07,580 --> 00:37:09,350 the continents had wrenched apart, 647 00:37:09,420 --> 00:37:12,350 and sea level rose. 648 00:37:12,420 --> 00:37:14,650 Mountain building slowed down, 649 00:37:14,720 --> 00:37:18,390 and so did rainfall and erosion. 650 00:37:18,460 --> 00:37:20,860 But co2-spewing volcanic eruptions, 651 00:37:20,930 --> 00:37:26,530 especially in the mid-ocean rift zones, did not. 652 00:37:26,600 --> 00:37:28,300 When continents are splitting apart 653 00:37:28,370 --> 00:37:30,340 and you have more sea floor spreading, 654 00:37:30,400 --> 00:37:32,770 you're adding more co2 to the atmosphere, 655 00:37:32,840 --> 00:37:35,570 and it's not being removed as quickly 656 00:37:35,640 --> 00:37:39,140 by weathering of the continents, 657 00:37:39,210 --> 00:37:41,680 so it's warmer during those periods. 658 00:37:43,750 --> 00:37:46,280 Temperatures rose to a balmy 54 degrees 659 00:37:46,350 --> 00:37:49,990 at the north and south Poles. 660 00:37:50,060 --> 00:37:52,490 The climate so agreed with the dinosaurs 661 00:37:52,560 --> 00:37:56,490 that they dominated life on Earth for millions of years. 662 00:37:58,430 --> 00:38:01,630 Then, 65 million years ago, 663 00:38:01,700 --> 00:38:05,400 a massive meteorite impact suddenly ended their reign. 664 00:38:12,480 --> 00:38:14,980 The meteorite gouged out a huge crater 665 00:38:15,050 --> 00:38:16,680 over 100 miles across 666 00:38:16,750 --> 00:38:20,320 with the town of Chicxulub, Mexico, at its center. 667 00:38:23,560 --> 00:38:27,060 The city of Merida also lies within the crater, 668 00:38:27,130 --> 00:38:30,900 which was buried by sediment millions of years ago 669 00:38:30,960 --> 00:38:34,300 and only discovered by chance as geologists explored for oil 670 00:38:34,370 --> 00:38:36,200 in the 1970s. 671 00:38:41,140 --> 00:38:43,880 The crater and its surroundings are also the site 672 00:38:43,940 --> 00:38:47,310 of the great cities built by the ancient Maya. 673 00:38:47,380 --> 00:38:50,180 But none of the human drama playing out in this region 674 00:38:50,250 --> 00:38:51,780 would have been possible 675 00:38:51,850 --> 00:38:53,820 if it weren't for the killer meteorite 676 00:38:53,890 --> 00:38:55,550 that struck here, 677 00:38:55,620 --> 00:38:58,860 wiping out the dinosaurs. 678 00:38:58,930 --> 00:39:01,630 Their extinction opened an evolutionary door 679 00:39:01,690 --> 00:39:04,360 for mammals like US to evolve. 680 00:39:07,500 --> 00:39:09,730 But 65 million years ago, 681 00:39:09,800 --> 00:39:11,800 the earthly stage was far from set 682 00:39:11,870 --> 00:39:14,840 for the entrance of people. 683 00:39:14,910 --> 00:39:19,280 Co2 levels and temperatures were much too high. 684 00:39:19,350 --> 00:39:23,610 Luckily for US, plate tectonics built the most massive structure 685 00:39:23,680 --> 00:39:27,590 on Earth to make the climate human-friendly: 686 00:39:27,650 --> 00:39:32,220 The great Himalaya range. 687 00:39:32,290 --> 00:39:36,590 About 60 million years ago, India, once a massive island, 688 00:39:36,660 --> 00:39:40,260 rammed Asia, and the building of the Himalaya began. 689 00:39:42,940 --> 00:39:44,840 As the himalayas grew, 690 00:39:44,900 --> 00:39:49,210 a great block of land rose up behind the range. 691 00:39:49,280 --> 00:39:51,340 It formed the Tibetan plateau 692 00:39:51,410 --> 00:39:55,280 and even raised the land as far to the north as Mongolia, 693 00:39:55,350 --> 00:39:58,750 more than 1,000 miles away. 694 00:39:58,820 --> 00:40:02,490 Since then, the Earth's climate has never been the same. 695 00:40:06,360 --> 00:40:09,230 There's a real belief amongst geologists 696 00:40:09,300 --> 00:40:12,500 that the growth of the Himalaya in Tibet 697 00:40:12,570 --> 00:40:15,570 over the last 60 million years 698 00:40:15,640 --> 00:40:18,270 has led to major changes in the global climate. 699 00:40:20,670 --> 00:40:23,570 The Indian monsoon is created 700 00:40:23,640 --> 00:40:26,540 when warm air from the Indian ocean 701 00:40:26,610 --> 00:40:28,610 meets the mountains of the Himalaya 702 00:40:28,680 --> 00:40:32,680 and dumps the rain on that mountain front. 703 00:40:32,750 --> 00:40:35,790 Prior to the formation of the Himalaya in Tibet, 704 00:40:35,860 --> 00:40:37,460 there was no monsoon. 705 00:40:37,520 --> 00:40:40,190 There was no barrier to the northward progress 706 00:40:40,260 --> 00:40:42,330 of the moist Indian ocean air. 707 00:40:45,900 --> 00:40:48,570 The new monsoon began dumping rain and snow 708 00:40:48,640 --> 00:40:52,240 on the growing mountains of Asia. 709 00:40:52,310 --> 00:40:55,170 This eroded the rocks and changed the chemical balance 710 00:40:55,240 --> 00:40:58,580 in the atmosphere. 711 00:40:58,650 --> 00:41:02,180 Massive amounts of co2 were removed from the air, 712 00:41:02,250 --> 00:41:05,880 so much that the global climate began to cool. 713 00:41:08,520 --> 00:41:11,590 It was the first time in hundreds of millions of years 714 00:41:11,660 --> 00:41:16,130 that the Earth's climate cooled so deeply. 715 00:41:16,200 --> 00:41:19,160 But before we humans made our appearance, 716 00:41:19,230 --> 00:41:22,600 plate tectonics had a few more modifications to make. 717 00:41:25,440 --> 00:41:27,100 All right, here. Here we go. 718 00:41:27,170 --> 00:41:28,640 In Antarctica, 719 00:41:28,710 --> 00:41:32,010 scientists made the startling discovery 720 00:41:32,080 --> 00:41:34,550 that this lonely continent at the bottom of the world 721 00:41:34,610 --> 00:41:38,650 was once connected to Australia. 722 00:41:38,720 --> 00:41:41,590 Then 40 million years ago, 723 00:41:41,650 --> 00:41:44,260 the land masses rifted apart, 724 00:41:44,320 --> 00:41:49,060 completely changing ocean currents in the region. 725 00:41:49,130 --> 00:41:50,830 Over the last 40 million years, 726 00:41:50,900 --> 00:41:54,000 Antarctica became an isolated continent down there, 727 00:41:54,070 --> 00:41:58,900 and so the circum-antarctic current formed, 728 00:41:58,970 --> 00:42:01,970 which isolated that continent so it could cool 729 00:42:02,040 --> 00:42:03,710 and start to grow an ice sheet. 730 00:42:07,350 --> 00:42:08,480 For the first time, 731 00:42:08,550 --> 00:42:10,650 Antarctica became frozen with ice, 732 00:42:10,720 --> 00:42:13,280 up to 15,000 feet thick, 733 00:42:13,350 --> 00:42:17,820 dropping global temperatures even more. 734 00:42:17,890 --> 00:42:20,560 And then, 3 million years ago, 735 00:42:20,630 --> 00:42:24,460 a new land bridge welded south and North America together. 736 00:42:26,700 --> 00:42:29,130 Before that, the two continents were separated 737 00:42:29,200 --> 00:42:32,970 by the ancient Panama seaway. 738 00:42:33,040 --> 00:42:35,710 As plate tectonics joined them together, 739 00:42:35,780 --> 00:42:40,240 ocean currents were radically rerouted once again. 740 00:42:40,310 --> 00:42:43,750 The Gulf stream, instead of going into the pacific ocean, 741 00:42:43,820 --> 00:42:47,950 it actually was then redirected upward in the Atlantic, 742 00:42:48,020 --> 00:42:53,620 bringing more moisture up into the north Atlantic, 743 00:42:53,690 --> 00:42:56,030 and that's a source of moisture for ice 744 00:42:56,100 --> 00:43:00,300 on the continents up there. 745 00:43:00,370 --> 00:43:02,900 By 2 1/2 million years ago, 746 00:43:02,970 --> 00:43:07,140 temperatures plunged so much that the pleistocene ice ages 747 00:43:07,210 --> 00:43:10,240 were triggered, 748 00:43:10,310 --> 00:43:12,240 and in this ice age world, 749 00:43:12,310 --> 00:43:14,780 when freezing glacial periods alternated 750 00:43:14,850 --> 00:43:17,720 with much warmer interglacials, 751 00:43:17,780 --> 00:43:20,120 the story of human evolution unfolded 752 00:43:20,190 --> 00:43:22,190 in the east African rift. 753 00:43:28,290 --> 00:43:30,730 Humans have lived through eight major ice ages 754 00:43:30,800 --> 00:43:33,500 over the past million years. 755 00:43:33,570 --> 00:43:37,230 The last glacial period ended 10,000 years ago, 756 00:43:37,300 --> 00:43:42,140 and we are now at the tail end of an interglacial. 757 00:43:42,210 --> 00:43:45,140 The climate has been warm on average, 758 00:43:45,210 --> 00:43:48,210 but with enough variation to profoundly affect people 759 00:43:48,280 --> 00:43:52,450 and even civilizations. 760 00:43:52,520 --> 00:43:56,020 Once we entered the warm period we're in now 761 00:43:56,090 --> 00:43:58,960 that started about 10,000 years ago, 762 00:43:59,030 --> 00:44:02,090 the changes in climate have been relatively smaller 763 00:44:02,160 --> 00:44:04,400 than the ice ages, 764 00:44:04,460 --> 00:44:06,060 but they've been big enough 765 00:44:06,130 --> 00:44:10,400 that there were droughts and floods and cold periods 766 00:44:10,470 --> 00:44:12,500 and little mini ice ages. 767 00:44:12,570 --> 00:44:14,540 And that people were still migrating 768 00:44:14,610 --> 00:44:17,480 and still having to adapt. 769 00:44:19,780 --> 00:44:23,480 Researchers studying past climate changes 770 00:44:23,550 --> 00:44:26,050 in Guatemala found that long droughts occurred 771 00:44:26,120 --> 00:44:28,650 at the height of the ancient Maya civilization, 772 00:44:28,720 --> 00:44:33,760 from 3,000 to 1,000 years ago. 773 00:44:33,830 --> 00:44:35,560 This may have been a big factor 774 00:44:35,630 --> 00:44:38,700 in the Maya civilization's mysterious collapse. 775 00:44:44,070 --> 00:44:47,610 Because global warming is again creating serious problems 776 00:44:47,670 --> 00:44:49,740 for people and ecosystems, 777 00:44:49,810 --> 00:44:52,940 scientists are engaged in an urgent effort 778 00:44:53,010 --> 00:44:55,310 to study past climate changes 779 00:44:55,380 --> 00:45:00,450 in order to predict what might happen in the future. 780 00:45:00,520 --> 00:45:03,450 One of their best tools is the study of gases 781 00:45:03,520 --> 00:45:05,620 that cause global warming, 782 00:45:05,690 --> 00:45:10,360 especially carbon dioxide, or co2. 783 00:45:10,430 --> 00:45:14,030 These gases are detected in ancient glacial ice 784 00:45:14,100 --> 00:45:17,170 hundreds of thousands of years old in Antarctica. 785 00:45:19,510 --> 00:45:22,310 Atmospheric gases get trapped in the ice, 786 00:45:22,380 --> 00:45:25,210 and you get these trapped bubbles of atmosphere 787 00:45:25,280 --> 00:45:27,080 that are preserved, 788 00:45:27,150 --> 00:45:29,780 and so when you take the ice core, 789 00:45:29,850 --> 00:45:34,820 you have this sort of ancient atmosphere. 790 00:45:34,890 --> 00:45:38,420 And so they can release that and measure the amount of co2 791 00:45:38,490 --> 00:45:40,060 that was around. 792 00:45:40,130 --> 00:45:44,030 And also how it changed since the last ice age. 793 00:45:45,830 --> 00:45:49,870 So we know from the ice cores that the natural level of co2 794 00:45:49,940 --> 00:45:52,440 should be about 280 parts per million, 795 00:45:52,510 --> 00:45:55,770 and today it's about 390 parts per million, 796 00:45:55,840 --> 00:45:59,710 as humans have been burning fossil fuels and releasing co2. 797 00:46:03,580 --> 00:46:05,220 That's a really big rise. 798 00:46:05,280 --> 00:46:09,190 We've never seen this rapid a rise of co2 799 00:46:09,260 --> 00:46:10,820 in the atmosphere 800 00:46:10,890 --> 00:46:13,560 over, you know, 100 million years. 801 00:46:17,530 --> 00:46:20,930 So it appears that one natural Earth system, 802 00:46:21,000 --> 00:46:22,330 the climate, 803 00:46:22,400 --> 00:46:25,440 may indeed be entering a period of intense upheaval. 804 00:46:33,380 --> 00:46:35,850 What about the other natural Earth systems, 805 00:46:35,920 --> 00:46:39,780 like those that cause earthquakes and volcanoes? 806 00:46:39,850 --> 00:46:43,320 Iceland's most active volcano has started erupting. 807 00:46:43,390 --> 00:46:44,560 Have any of these 808 00:46:44,620 --> 00:46:46,960 begun a period of increased activity? 809 00:46:47,030 --> 00:46:50,460 Has been spewing ash and smoke 12 miles into the air. 810 00:46:52,160 --> 00:46:54,060 Looking back 100 years, 811 00:46:54,130 --> 00:46:56,530 the number of volcanic eruptions each year 812 00:46:56,600 --> 00:46:59,640 has actually held steady. 813 00:46:59,710 --> 00:47:03,170 In general, the public only hears about volcanic eruptions 814 00:47:03,240 --> 00:47:07,480 when they're particularly big, when they kill people, 815 00:47:07,550 --> 00:47:11,750 but, in fact, there are usually couple dozen volcanic eruptions 816 00:47:11,820 --> 00:47:14,650 going on every month. 817 00:47:14,720 --> 00:47:18,620 And some volcanoes have been erupting for dozens of years, 818 00:47:18,690 --> 00:47:20,290 like kilauea... 819 00:47:20,360 --> 00:47:24,560 Or even hundreds or thousands of years 820 00:47:24,630 --> 00:47:27,600 like Aetna in Italy. 821 00:47:27,670 --> 00:47:29,800 So there is a lot of variation 822 00:47:29,870 --> 00:47:34,310 in terms of sometimes we have really big volcanic eruptions, 823 00:47:34,370 --> 00:47:39,380 and then we might go for months or years without one of those. 824 00:47:39,450 --> 00:47:41,510 But, in fact, volcanoes are erupting 825 00:47:41,580 --> 00:47:43,580 around the Earth all the time. 826 00:47:49,260 --> 00:47:52,220 A similar scenario holds for earthquakes. 827 00:47:56,260 --> 00:47:59,300 The number of big quakes greater than magnitude 7 828 00:47:59,370 --> 00:48:01,130 averages 18 per year. 829 00:48:01,200 --> 00:48:03,300 At least 250 people have died 830 00:48:03,370 --> 00:48:06,170 after a major earthquake hit southwestern Pakistan. 831 00:48:06,240 --> 00:48:07,400 One of these quakes 832 00:48:07,470 --> 00:48:10,040 is higher than magnitude 8 each year. 833 00:48:12,210 --> 00:48:17,720 This number has held steady since the year 1900. 834 00:48:17,780 --> 00:48:20,680 But it may seem that earthquakes have become more frequent 835 00:48:20,750 --> 00:48:22,220 for several reasons. 836 00:48:22,290 --> 00:48:23,620 Yo! 837 00:48:23,690 --> 00:48:25,090 Excuse me! 838 00:48:25,160 --> 00:48:29,030 First, more are being recorded and pinpointed. 839 00:48:29,100 --> 00:48:34,030 More than 8,000 stations listen for quakes worldwide. 840 00:48:34,100 --> 00:48:39,540 In 1931, there were just 350. 841 00:48:39,610 --> 00:48:41,670 Earthquakes also seem more numerous 842 00:48:41,740 --> 00:48:43,710 because of the soaring population 843 00:48:43,780 --> 00:48:47,210 and near-instant reporting of news worldwide. 844 00:48:50,420 --> 00:48:55,250 The earthquake that killed 1/4 million people in Haiti 845 00:48:55,320 --> 00:48:58,920 would only have killed 1/10 that number 100 years ago, 846 00:48:58,990 --> 00:49:00,430 and we wouldn't have known about it. 847 00:49:00,490 --> 00:49:02,960 This is some of what I saw on the streets. 848 00:49:03,030 --> 00:49:04,960 Now we hear about these things instantly. 849 00:49:05,030 --> 00:49:07,560 We have the live footage of the tsunamis 850 00:49:07,630 --> 00:49:09,570 arriving on the Japanese coast, 851 00:49:09,640 --> 00:49:11,040 and the whole world knows about it. 852 00:49:14,370 --> 00:49:16,840 The recorded number of tsunamis has increased 853 00:49:16,910 --> 00:49:19,010 in the past 100 years, 854 00:49:19,080 --> 00:49:24,420 but scientists attribute this to ever-improving detection. 855 00:49:24,480 --> 00:49:27,050 And with better warning systems being installed, 856 00:49:27,120 --> 00:49:31,360 the loss of life is decreasing. 857 00:49:31,420 --> 00:49:33,820 So do scientists see an uptick 858 00:49:33,890 --> 00:49:36,360 in increased geological activity? 859 00:49:39,270 --> 00:49:41,430 No, the Earth's doing the same thing 860 00:49:41,500 --> 00:49:43,670 it's been doing for billions of years. 861 00:49:43,740 --> 00:49:45,800 We notice the events more 862 00:49:45,870 --> 00:49:48,710 because our more complex society 863 00:49:48,770 --> 00:49:52,710 and our far more populated planet 864 00:49:52,780 --> 00:49:55,180 are much more vulnerable to these disasters. 865 00:49:58,280 --> 00:50:00,600 There's no real evidence that we're living through a period 866 00:50:00,650 --> 00:50:02,050 of enhanced activity. 867 00:50:02,120 --> 00:50:03,690 In any one area, 868 00:50:03,760 --> 00:50:08,490 there may be regions where we have a few more earthquakes 869 00:50:08,560 --> 00:50:12,500 for a few hundred years, and then after that clustering, 870 00:50:12,570 --> 00:50:14,700 seismicity will die away. 871 00:50:14,770 --> 00:50:17,570 But on a planet-wide scale, there's no evidence for that. 872 00:50:20,810 --> 00:50:23,810 Looking deeper into Earth's geologic past, 873 00:50:23,880 --> 00:50:25,710 far bigger upheavals have occurred 874 00:50:25,780 --> 00:50:29,050 than anything known by humans. 875 00:50:29,120 --> 00:50:32,080 A supervolcano thousands of times bigger 876 00:50:32,150 --> 00:50:35,250 than the huge mount Saint Helens eruption of 1980 877 00:50:35,320 --> 00:50:39,390 went off at yellowstone 640,000 years ago. 878 00:50:41,460 --> 00:50:45,930 Supervolcanoes are exceedingly rare in human terms. 879 00:50:46,000 --> 00:50:48,770 None have erupted for 26,000 years. 880 00:50:52,200 --> 00:50:55,870 Earth's history book chronicles other massive upheavals 881 00:50:55,940 --> 00:50:59,540 like the siberian traps. 882 00:50:59,610 --> 00:51:04,150 There was snowball Earth, when the whole world froze over. 883 00:51:04,220 --> 00:51:05,950 In more recent times, 884 00:51:06,020 --> 00:51:09,020 our distant ancestors experienced the bitter cold 885 00:51:09,090 --> 00:51:10,990 of the ice ages, 886 00:51:11,060 --> 00:51:14,390 when Chicago lay under a mile-thick sheet of ice. 887 00:51:16,860 --> 00:51:20,660 If planet Earth were acting up more than usual right now, 888 00:51:20,730 --> 00:51:22,200 it would barely register 889 00:51:22,270 --> 00:51:24,700 in the annals of major earthly events. 890 00:51:26,340 --> 00:51:28,670 The exception is the climate, 891 00:51:28,740 --> 00:51:31,540 which is changing in ways never before seen 892 00:51:31,610 --> 00:51:34,380 in the geologic record. 893 00:51:34,450 --> 00:51:38,080 People may have some influence over this process, 894 00:51:38,150 --> 00:51:40,050 but deep Earth processes 895 00:51:40,120 --> 00:51:42,920 like earthquakes and volcanic eruptions 896 00:51:42,990 --> 00:51:46,960 are beyond anyone's control. 897 00:51:47,030 --> 00:51:48,660 So scientists are focusing on 898 00:51:48,730 --> 00:51:51,360 ways to live with these powerful forces 899 00:51:51,430 --> 00:51:54,630 and reduce their threats. 900 00:51:54,700 --> 00:51:56,420 The public would love it if we could provide 901 00:51:56,440 --> 00:51:58,900 short-term predictions of hours to days 902 00:51:58,970 --> 00:52:01,610 before an earthquake, and we can't do that. 903 00:52:01,670 --> 00:52:05,740 But what we can do is provide long-term estimates... 904 00:52:05,810 --> 00:52:07,810 Decadal estimates, perhaps. 905 00:52:07,880 --> 00:52:10,750 That should be important to US, to our society, 906 00:52:10,820 --> 00:52:12,450 to plan for these events. 907 00:52:14,620 --> 00:52:17,250 In my lifetime, there's a 3/4 chance 908 00:52:17,320 --> 00:52:21,060 there will be a major earthquake in the bay area where I live, 909 00:52:21,130 --> 00:52:23,560 and that should be enough to encourage me 910 00:52:23,630 --> 00:52:25,900 to plan wisely for that earthquake 911 00:52:25,970 --> 00:52:27,760 that I need to expect. 912 00:52:33,570 --> 00:52:36,610 With earthquake predictions still in the future, 913 00:52:36,680 --> 00:52:38,610 earthquake-prone Japan has developed 914 00:52:38,680 --> 00:52:43,350 the world's first earthquake and Tsunami early warning system. 915 00:52:43,420 --> 00:52:47,990 Its first major test came with the massive earthquake in 2011. 916 00:52:50,190 --> 00:52:52,290 Residents of Tokyo were warned 917 00:52:52,360 --> 00:52:55,060 eight to nine seconds before the quake hit. 918 00:52:55,130 --> 00:52:57,460 At 2:46 in the afternoon. 919 00:52:57,530 --> 00:53:00,030 The shaking went on for more than 2 minutes. 920 00:53:00,100 --> 00:53:01,700 The closest major city, sendai... 921 00:53:01,770 --> 00:53:04,770 Residents of the nearest coastal city of sendai 922 00:53:04,840 --> 00:53:07,440 heard Tsunami warnings eight minutes before 923 00:53:07,510 --> 00:53:09,770 the 33-foot Tsunami came ashore. 924 00:53:12,850 --> 00:53:14,950 Japan's advanced state of preparedness 925 00:53:15,010 --> 00:53:18,280 and strong building codes were the critical factors 926 00:53:18,350 --> 00:53:22,650 in saving countless lives during this disaster. 927 00:53:22,720 --> 00:53:24,120 And the early warning system 928 00:53:24,190 --> 00:53:28,230 saved an untold number of lives as well. 929 00:53:31,200 --> 00:53:34,730 The Japan meteorological agencies early warning system 930 00:53:34,800 --> 00:53:38,270 also doubles as Japan's volcanic eruption warning system. 931 00:53:40,370 --> 00:53:44,270 Eruptions are easier to predict than earthquakes. 932 00:53:44,340 --> 00:53:47,140 We are getting better all the time 933 00:53:47,210 --> 00:53:49,110 at predicting volcanic eruptions, 934 00:53:49,180 --> 00:53:52,920 but it's by no means perfect. 935 00:53:52,990 --> 00:53:57,350 And it's still a very difficult thing to do. 936 00:53:57,420 --> 00:53:59,860 We have much better instrumentation. 937 00:53:59,930 --> 00:54:03,390 We can measure the inflation of the ground. 938 00:54:03,460 --> 00:54:06,900 Seismographs see how magma is moving up. 939 00:54:06,970 --> 00:54:11,130 Even temperatures of fumaroles, changes in the gases. 940 00:54:11,200 --> 00:54:13,440 So we are getting better all the time. 941 00:54:22,180 --> 00:54:24,680 Meanwhile Earth's inner and outer forces 942 00:54:24,750 --> 00:54:28,420 will keep reworking the planet, 943 00:54:28,490 --> 00:54:31,320 from the center of the inner core 944 00:54:31,390 --> 00:54:34,890 to the highest peaks on the surface. 945 00:54:34,960 --> 00:54:37,430 No other planet known to US 946 00:54:37,500 --> 00:54:41,800 has so many different natural forces at work. 947 00:54:41,870 --> 00:54:43,630 The Earth we see today 948 00:54:43,700 --> 00:54:47,440 has been 4 1/2 billion years in the making 949 00:54:47,510 --> 00:54:51,340 and has never looked quite this way before, 950 00:54:51,410 --> 00:54:55,950 and it will never look the same again. 951 00:54:56,010 --> 00:54:59,150 I think the way the Earth looks now as a planet 952 00:54:59,220 --> 00:55:02,620 is unique in history, 953 00:55:02,690 --> 00:55:05,320 as is almost every period in geologic history. 954 00:55:05,390 --> 00:55:08,390 The Earth is constantly undergoing change. 955 00:55:08,460 --> 00:55:09,460 What are the Greens? 956 00:55:09,530 --> 00:55:10,770 The Greens are country roads, 957 00:55:10,800 --> 00:55:12,300 and the yellows are local roads. 958 00:55:12,360 --> 00:55:14,430 From a geologist's point of view, 959 00:55:14,500 --> 00:55:17,530 the Earth is really, really interesting 960 00:55:17,600 --> 00:55:22,570 because, on Earth, we see all the major processes 961 00:55:22,640 --> 00:55:27,410 that form the surface of a planet actually going on. 962 00:55:27,480 --> 00:55:30,510 We have volcanism. 963 00:55:30,580 --> 00:55:34,550 We have impact craters formed not that long ago. 964 00:55:34,620 --> 00:55:36,550 We have an atmosphere, 965 00:55:36,620 --> 00:55:40,520 which means we have liquid water. 966 00:55:40,590 --> 00:55:44,130 We have wind. We have erosion. 967 00:55:44,200 --> 00:55:46,500 We have plate tectonics on Earth 968 00:55:46,570 --> 00:55:50,600 which appears to be unique in the solar system. 969 00:55:50,670 --> 00:55:55,840 So it's very geologically diverse and very dynamic. 970 00:55:55,910 --> 00:55:58,440 So I think we are lucky, actually, to live here.